I. Field of the Invention
The present invention is directed generally to controlling auxiliary pusher or trailer load support axles for utility or load hauling vehicles such as dump trucks, over-the-road tractors and trailers, transit concrete mixing trucks or refuse collecting vehicles. The auxiliary pusher or trailer axle systems are used to selectively deploy auxiliary wheels in a ground-engaging, load-supporting position or to retract them to an elevated or stowed position. The systems are normally operated by forces generated by hydraulic cylinders or pneumatic springs and the amount of load support may be varied by varying cylinder pressure. The present invention more particularly relates to the automatic control of the relative amount of shared support, in keeping with the vehicle loading weight so that the axle loading of the vehicle is compensated accordingly to optimize load distribution.
II. Related Art
Transit concrete mixers are typical among those commercial vehicles that are called upon to haul a variety of load weights at different times. Such vehicles further typically include a single set of forward steering wheels and a plurality of rear, load-supporting drive axles carrying dual wheel arrangements, all mounted on an elongated continuous chassis. The chassis length or distance between certain sets of dual wheel arrangements may further be adjustable in some models. For additional support, particularly in transit when loading exceeds a minimum amount, vehicles of the class typically are provided with one or more pivotally mounted, hydraulically or pneumatically operated, auxiliary axles able to operate between a raised or stowed position carried by the truck and in a load-bearing or deployed position wherein the auxiliary axle and its wheels share the load of the truck with the permanent steering and drive wheel system. Auxiliary axles mounted forward of the drive wheels of a vehicle are typically referred to as pusher axles and those mounted aft of the drive wheels are known as trailer or tag axles. Each auxiliary axle system includes two or more wheels and possibly a plurality of dual wheel axles in such systems, the wheels may be connected by one or more through or common shafts or be independently mounted on stub axles.
Not only does an auxiliary pusher or trailer axle system assist in balancing the load carried by the truck adding safety and convenience, it also enables the truck to carry a higher total payload than would otherwise be permitted by adding one or more additional load bearing axles to which a portion of the load may be distributed to meet legal load per-axle limitations. Because the load often varies, with time however, it is often desirable to adjust the pressure in the system deploying the auxiliary axle so that the axle loading and thus the distribution of weight to the various axles of the truck is maintained at an optimum to compensate for the total loading of the vehicle.
Examples of prior auxiliary axle systems utilized with transit concrete mixing vehicles include U.S. Pat. No. 4,195,856 to Larson et al, U.S. Pat. No. 4,705,133 to Christenson et al; U.S. Pat. No. 5,498,021 to Christenson and U.S. Pat. No. 5,549,322 to Hauri. Additional tag axle systems as applied to load hauling vehicles of the refuse collecting class can be found in U.S. Pat. No. 5,090,495 to Christenson; U.S. Pat. No. 5,597,174 to Christenson et al; and U.S. Pat. No. 5,713,42,4, also to Christenson.
While these and similar embodiments have been relatively successful over the years, prior pusher and tag or trailer axles have either had no provision for adjusting the pressure applied to the deployed axle or have had only manually operable systems for adjusting the pressure applied to the axle to adjust road force in response to estimated truck payload weights. Charts for adjusting such systems manually based on estimated data may be provided for drivers to follow. One such chart is shown in Table I below. The ability to adjust the hydraulic or pneumatic pressure utilized to lower and apply force to pusher and trailer axles over a rather wide bed range not only allows a transit mixer, for example, to carry a larger legal load of concrete while complying with the required state highway weight laws, but it also allows the system to properly balance a variety of different sized loads. For example, if a driver hauls a ten-yard load of concrete (generally given as 40,000 pounds) on one load and only five yards (20,000 pounds) on another load, clearly the downward force or load carried by an auxiliary pusher or trailer axle should be readjusted downward (lowered) to maintain proper shared load balance coordination among the axles. Likewise, when the driver gets to the jobsite and the load is discharged, the pressure to the trailer axle should be reduced to a minimum or the axle prestowed by manual adjustment.
Manual systems, however, have drawbacks. In certain cases, if the driver fails to readjust the pressure for individual loads, the mixer truck may not comply with state axle weight limitations and, moreover, if the pressure is not properly reduced, the lift exerted by the pusher or trailer axle may reduce traction in the rear drive wheels of the truck. In addition, the estimated payload weights may not be as close to the actual values as desired.
Of course, the same type of load variation and estimation problems arise with respect to the collection of refuse, with large dump trucks, log-hauling vehicles or in other load hauling situations in which the weight of the payload can vary over a fairly wide range with respect to the use of the vehicle. In view of the present state of the art, there remains a need for an auto-responsive control system to modulate the application of force by auxiliary axle systems by automatically adjusting applied
hydraulic or pneumatic pressure applied to the system. This would improve both the versatility and the safety of the vehicles.
Accordingly, it is a primary object of the present invention to provide an automated control system for auxiliary axles that is responsive to changes in vehicle payload weight.
It is a further object of the present invention to provide an automated system for controlling the deployment pressure to auxiliary axles including each pusher or trailer axle of a vehicle based on the then-present measured payload weight.
It is a still further object of the present invention to provide an automated deployment control system for auxiliary axles which further indicates present auxiliary axle state and whether the axle should be deployed or stowed.
Yet another object of the present invention is to provide an automated auxiliary axle deployment pressure control system that utilizes real-time payload weight distribution.
Another object of the present invention is to provide an automated auxiliary axle control system that coordinates real-time, payload weight distribution with data from a permanent stored record of unloaded vehicle parameters to provide desired real-time axle/weight distribution.
Other objects or advantages will become apparent to those skilled in the art upon familiarization with the specification, claims and drawings contained herein.
The present invention provides a method and apparatus for automated auxiliary pusher (forward) or trailer (rearward deployed) axle pressure control. The invention supplies the ability to automatically adjust road support force applied by pusher or trailer wheels in each set of such wheels and is very useful in a vehicle subject to time-variable loading. The invention applies equally to hydraulically or pneumatically operated pusher and/or trailer wheels and the wheels of each axle or set can be controlled in accordance with the invention. The system can also be using auxiliary support wheels mounted and configured to operate separately on stub axles or in unison on single or multiple through axles. The control system is particularly suitable for use with a class of vehicles including any heavy-duty hauling truck or trailer accustomed to payload variations, examples including transit concrete mixers, dump trucks, log haulers and refuse collecting vehicles. Generally, not only does the total load change but the distribution of the load among vehicle axles may also vary greatly.
The control system of the invention includes one or more integral devices or frame scales which enable accurate weight measurement of amount and distribution the carried payload such as the weight of a load of concrete in a mixing drum. The measurements may be sensed continually, i.e., metered on a real-time basis and may include measurements of the weight carried by each axle or axle group. These measurements then, in turn, are used in the control of the hydraulic or pneumatic pressure applied to one or more deployed sets of pusher and/or trailer wheels, and/or other aspects of a vehicle suspension system thereby compensating for light loads, intermediate and maximum loads and load distribution. In the case of concrete, for example, the direct accurate weight measurement, of course, has the added value over volume based measurements in that it further compensates for the difference in the weight per yard (density) of various mixes not taken into consideration by previous manual systems that predicted adjustment based on yardage (volume) alone.
Because every axle or axle set can be metered and the system can have the ability to modulate pressure to individual auxiliary wheel sets and possibly individual auxiliary wheels on either side of the vehicle as well, this allows the invention to function as an auto leveling system or to compliment such a system by adjusting relative load distribution among support axles and possibly individual wheels.
Of course, the system of the invention also recognizes the lightly loaded or unloaded truck or trailer condition which can be utilized to reduce the pressure to a minimum or prompt the driver to stow the pusher or trailer wheels completely. Thus, when the drum of a mixing vehicle or load compartment of another vehicle is empty, the pressure is reduced to a minimum setting, i.e., 900-1000 psi typically for a hydraulic system and 0-120 psi for a pneumatic spring bellows system or the axle raised and stowed. Conversely, the system may prompt the driver to lower raised auxiliary or trailer axles when the load weight reaches a certain given minimum amount, depending on the vehicle involved. The control system itself can also be configured to automatically raise and lower the pusher or trailer axles if desired.
Any conventional vehicle-mounted weighing system, including strain gauges, leverage devices and beam type scales or load cells, etc., can be used and, in one embodiment, the system includes a chassis/axle balanced beam differential system which measures chassis/axle gap variations at several points and yields an electrical output signal which can be utilized as an input to a control system used to control a pneumatic or hydraulic pressure modulating valve automatically. Onboard frame scale systems including embodiments that may be leaf-spring mounted, air spring or axle mounted are available, for example, from Weigh-Right of Hutchinson, Kansas and other manufacturers of such systems. If deployment/storage is not automatic, audio and/or visual signals may be utilized to alert the driver of the vehicle, as necessary, to deploy or stow trailer and/or pusher axles as needed.
The control system itself contains an amount of pre-programmed computer data relating to final sizes and weight parameters of the unloaded vehicle typically stored on a computer card located in an enclosure and which is integral to the hydraulic system. The card is programmed for the particular vehicle as manufactured and contains all the necessary fixed parameters and data to utilize real-time weight signals to accomplish the correct control utilizing pressure modulation.
Of course, the system is also configured so that if it experiences a malfunction, the auxiliary wheels may be deployed and adjusted using standard manual operating system as a back up or another alternate system can also be used.